SQL trigger- only insert select details

I have a trigger shown in the snippet,

It inserts the records in opdetm joined by opheadm.order_no = opdetm.order_no, into opdetm_audit when opheadm's status is updated to 9,

what i want to add now is that it will only add the opdetm records that do not exist in opdetm_audit2 (this is not a typo, there is an audit and an audit2 table)
joined by
opdetm.order_no = opdetm_audit2.order_no and
opdetm.order_line_no = opdetm_audit2.order_line_no,

ALTER TRIGGER [scheme].[metauddel]
ON [scheme].[opheadm]
AFTER UPDATE
AS
BEGIN
-- SET NOCOUNT ON added to prevent extra result sets from
-- interfering with SELECT statements.
SET NOCOUNT ON;
IF UPDATE (status)